The construction of the faucets of the type considered requires that the cartridge has to function as a hydraulic piston does so that the correct amount of contact pressure can be applied between the fixed valve plate and the movable valve plate of the faucet. The cartridge section on which the water pressure is applied must be limited so that excessive contact pressure does not develop. Consequently, the body of the faucet has required expensive work operations of deep undercutting at the section that receives the cartridge to limit the area that is exposed to the inlet water pressure.
Secondly, there are difficulties in accurately placing the fixed valve plate in an operatively fixed part of the cartridge. The valve plates are often made through processes of sinterization of ceramic materials where it is not possible to assure the effective dimensions of the product unless there are great relative tolerances that are proportional to the same dimensions. The smallest tolerance that is practically achieved in the diameter of a valve plate of normal dimensions can typically amount to 0.6 mm. This tolerance must be taken into consideration when producing the seat which is constructed to receive a valve plate of this type. Due to the manufacturing tolerances, the seats are often oversized so that the valve plates are placed with enough clearance to create a certain amount of gap space. During the operation of the faucet, the fixed valve plate can undergo lateral motion allowed by the gap thereby wearing on the seal gaskets on which it sits, and on the other hand, rendering the designed geometry of the system to be imperfect. In other words, the flow and mix curves designed into the faucet are not followed exactly due to the mispositioning and motion of the fixed plate.
Further, in order to fix the fixed valve plate in its correct angular position, some deep slits must be made on its periphery. These slits must extend radially and engage with corresponding projections from the valve seat. Further, the presence of these deep slits weakens the valve plates that are, by their nature, fragile.
Furthermore, it is often desired to clamp the fixed valve plate and not simply place it on the seal gasket of the seat. The operation of clamping by means of a central screw makes the process of mounting relatively onerous, and further, it requires that there be a hole in the fixed valve plate. The presence of a hole weakens the fixed valve plate and intrudes into the area best reserved for the opening of the passage to have the most desired form.
What is needed is a mixing faucet construction of the type considered in such a way as to provide more accurate lateral and angular positioning of the fixed valve plate and a clamping mechanism for the fixed plate while controlling the compression pressure due to the hydraulic pressure acting on the cartridge.